1. Field of the Invention
The invention relates to a method of improving the color of tall oil rosin esters.
2. Brief Description of the Prior Art
The prior art literature is replete with descriptions of methods for esterifying rosin with a polyol. Representative of such literature are the U.S. Pat. Nos. 1,696,337; 1,697,530; 1,734,987; 1,893,982; 2,327,009; 2,369,125; 2,409,332; 2,420,926; 2,434,168; 2,440,242; 2,536,600; 2,572,086; 2,590,910; 2,736,664; 2,864,810; and 3,780,012.
The large number of prior art references describing the esterification of rosin with a polyol is a reflection of the need in the art for improvements in methods of preparation. The method of the present invention is such an improvement, resulting in a more efficient process and a unique product composition.
As described by Sanderson in the U.S. Pat. No. 4,643,847 (1987), the use of a selective solvent refining process to improve the color of rosin by removing certain visible dark color bodies and latent color bodies from the rosin is disclosed in the earlier U.S. Pat. No. 1,715,085. The process comprises the formation of a solution of gasoline, rosin and furfural (C.sub.5 H.sub.4 O.sub.2), its cooling or refrigeration with resultant separation of furfural and coloring bodies, and the recovery of high grade rosin from the remaining solution. The wood rosin may be subjected to distillation prior to the solvent extraction.
Tall oil rosin contains color bodies or coloring matter visible to the naked eye and certain color bodies which are not normally visible to the naked eye, usually referred to as latent color bodies. The visible coloring matter in a tall oil rosin determines its grade and hence its value. The darker the rosin, the lower its grade and value. The presence of invisible or latent color bodies, while not affecting the apparent grade, is highly disadvantageous in the case of tall oil rosin since they render the polyol esters produced therefrom undesirable for use in the production of products where palest color of the product and stability of color are desired. In tall oil rosin, latent color bodies contained therein do not color the tall oil rosin until the rosin is esterified with pentaerythritol or like polyols to form an ester, or treated in the presence of oxygen, such as in the manufacture of hot melt adhesives.
The method of the present invention provides esters of rosin having improved, lighter colors which are stable, with a minimum of labor and cost.
U.S. Pat. No. 4,248,770 (Matsuo et al, 1981) discloses a method for preparing a stabilized tall oil rosin ester which comprises subjecting a rosin to disproportionation followed by purification and then esterification of the resulting purified disproportionated rosin with a polyol. The purification can be by distillation, crystallization or extraction.